The present invention relates in general to mesh screens and similar screening inserts and mechanisms which are used as part of a liquid control valve for separating out particulate matter from a flow of liquid, typically water, through the liquid control valve. More specifically, the present invention relates to the design of an in-line screen for a thermostatic valve, such as a thermostatically-controlled mixing valve, which would typically be used in conjunction with separate hot and cold water lines.
Single handle mixing valves are well known and common in the plumbing field. These valves provide a stream of mixed water from separate hot and cold water streams. However, these valves are subject to the inconvenience that may result from a sudden undesirable change in water temperature or pressure of the water in either of the lines supplying water to the valve. In some cases, the resulting change in the temperature of the mixed outlet water can result in discomfort to the user of the valve. The discomfort can be particularly pronounced when the valve is a shower mixing valve and the user is within the shower stall. A sudden pressure drop in the cold water line, such as that which frequently occurs when a toilet is flushed, will cause a sudden increase in the temperature of the shower water, requiring the user to move quickly away from the stream of water.
Several faucets and mixing valves have been developed in an attempt to reduce or eliminate this problem. U.S. Pat. No. 4,699,172 (issued Oct. 13, 1987 to MacDonald) provides a self-regulating valve assembly for combining pressurized hot and cold water to produce an output of mixed water having a preselected constant water temperature. The valve assembly comprises a housing having a valuing cavity, a hot water inlet leading to the valuing cavity, a cold water inlet leading to the valuing cavity, and a mixed water outlet passageway leading from the valuing cavity. A valve member translates in the valuing cavity and divides the cavity into two auxiliary chambers. A passageway through the valve member allows fluid to flow from each of the inlets to the outlet passageway at a rate that varies as the valve member translates. Passageways in the valve member permit a portion of the mixed water to flow into the auxiliary chambers. An auxiliary passageway is provided between each of the auxiliary chambers and the outlet passageway. A temperature responsive element is provided within the outlet passageway. In response to a deviation in the temperature of water in the mixing chamber, the temperature responsive element closes one of the auxiliary passageways, causing the valve member to translate until the water in the outlet passageway reaches the preselected temperature. U.S. Pat. No. 5,904,291 (issued May 18, 1999 to Knapp) also discloses a thermostatic faucet mixing valve which incorporates a thermostatic regulator for a single handle mixer valve which includes a sensor mounted in a mixed water chamber for sensing the temperature of the outlet water. In this case, the sensor is connected to a valve that is mounted in the cold water supply line in order to restrict the availability of cold water when the water in the hot water line is down below a set temperature.
While the present invention is described in the context of a thermostatic valve as part of a water delivery system, the specific focus of the present invention relates to an in-line screen which is used in each water line downstream from the inlet and upstream from the mixing chamber. While mesh screens are well known for water valves and faucets, one typical location is at the point of exit of the mixed stream of water, such as from a kitchen faucet where the exiting flow is aerated. Another possible location for such mesh screens is interior to the valve, such as that disclosed in U.S. Pat. No. 6,321,777 (issued Nov. 27, 2001 to Wu). In the '777 patent, a cylindrical water filter screen element (7) is positioned within the faucet body (2) between plug block (32) and water sealing washer (52).
In the context of a thermostatic valve, one location for a mesh screen would be around the cartridge. In the context of the present invention, and in the context of the prior art, the term “cartridge” is generally understood as referring to a multiple-component structure which can be handled as a single unit. This particular screen placement has been attempted and, as a result, a number of technical and performance facts have been discovered. First, in an effort to effectively separate out particulate matter from the flow of water, it has been learned that the openings in the mesh screen become plugged and, as a result, almost immediately there is a decrease in the flow rate. There obviously has to be a balance between the size of the screen mesh openings and the duration or length of use before the mesh screen has to be removed and cleaned. However, regardless of the cleaning cycle or interval, if the flow rate is decreased almost immediately as portions of the mesh screen become plugged with particulate, this is seen as a significant drawback to any such design. It would therefore be an improvement to this earlier mesh screen design and its arrangement within the valve if some significant portion of the screen could become plugged with particulate matter without any noticeable decrease in the (through) flow rate. The present invention provides such an improvement by the specific configuration of the disclosed screen and the configuration of the cooperating valve body and in particular the pocket where the disclosed screen is installed.
Another concern with the placement of a mesh screen around the cartridge is removal and replacement of the cartridge. Due to the close fit and limited clearance between the mesh screen and the exterior of the cartridge, the collection of particulate matter, as it becomes imbedded in the mesh, can make it difficult to install the cartridge. As an improvement to this earlier design and as an improvement to this issue in particular, the screen of the present invention is positioned downstream from the water inlet and the flow control mechanism in a separate portion of the valve body, without cooperating with or interfacing with any other structural portion other than the valve body pocket which receives the screen.
One issue related to the position of the mesh screen around the cartridge is that when the mesh screen is to be removed for cleaning, the cartridge must also be removed. When the cartridge is taken out of the housing body, the cooperating control handle may lose its calibration relative to the hot limit stop or setting. This is seen as a safety concern and this problem should be avoided if at all possible.
Another issue related to the arrangement of placing the mesh screen around the cartridge is the likelihood of once collected debris (i.e., separated particulate) falling off of the mesh screen and going right back into the interior of the valve body to simply be collected by the mesh screen all over again or possibly passing downstream such that it is not collected at all.
The screen of the present invention has an overall design which provides a number of features which are different from the structure of the prior mesh screen that is positioned around the cartridge. The benefits and improvements of the present invention encompass aspects of the structure of the screen as well as its placement within the surrounding valve structure, and the cooperating design of the surrounding valve structure, which in the preferred embodiment is the valve body of a thermostatic valve.